custom sort posts in archive/taxanomy page

Put something along these lines in your functions.php:

add_filter( 'pre_get_posts', 'custom_get_posts' );

function custom_get_posts( $query ) {

if( is_category() || is_archive() ) { 
$query->query_vars['orderby'] = 'name';
$query->query_vars['order'] = 'ASC';
}

return $query;
}

reference here (see the second answer)